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    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        // 目标获取obj

        function a(callback) {
            setTimeout(function() {
                let obj = {
                    code: 200,
                    data: {
                        str: 111
                    }
                }

                callback(obj)
            }, 1000)
        }

        // 1.没有传入callback  直接打印a()
        // console.log(a()) //undefined

        // 2.使用callback ES6没出之前
        a(function(res) {
            console.log(res)
        })
    </script>
</body>

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